1. Technical Field
This invention relates to a method and system for analysing and/or generating object models, and in particular to generating object models of a second type using object models of a first type.
2. Related Art
It is known that virtual object models of human bodies can be created, which provide for a human body representation in a computer-generated, virtual space. The models of such “virtual humans” are commonly referred to in the art as “avatars”.
One increasingly popular touted use of avatars is to have them model clothes on-line for use in on-line shopping applications. One problem is that for clothes to hang realistically on an avatar the computer needs to do very expensive cloth dynamics calculations. Cloth dynamics is slow and processor intensive, and is therefore not suitable for consumer-end computers or mobile devices.
Cloth dynamics methods are based on a physical simulation of the motion and properties of the cloth. Clothes are fitted by finding a physically stable configuration of the cloth. In D. Terzopoulos, J. C. Platt and H. Barr, (1987) Elastically Deformable Models, Computer Graphics (SIGGRAPH '97 proceedings), Addison-Wesley, 21, pp 205-214, 1987 there is presented a method based on treating the cloth as a continuous surface and expressing motion of an infinitesimal element of that surface as Lagrange equations. J. W. Eischen, S. Deng and T. G. Clapp (1996) in Finite-Element Modelling and control of Flexible Fabric Parts, Computer Graphics in Textiles and Apparel (IEEE Computer Graphics and Applications) pp 71-80, September 1996 use finite elements to model cloth, however, this method is unfeasibly expensive in terms of computational power. D. E. Breen, D. H. House and M. J. Wozny (1994), Predicting the Drape of Woven Cloth Using Interacting Particles, Computer Graphics (SIGGRAPH'94 proceedings), Addison-Wesley, pp 365-372, July 1994 represent cloth as a lattice of particles with forces between them represented as springs. These are the main cloth simulation methods. There have been various developments for each method, and P. Volani and N. Magnenat-Thalmann (2000), Virtual Clothing: Theory and Practice, Springer-Verlag 2000 presents an overview and also gives a state of the art cloth dynamics and clothing system.
In addition to the above-described cloth-dynamics approaches, there are also slow geometric methods for fitting clothes which do not take physics into account but use the geometry of the avatar as a basis for transforming the clothing, as described in, for example, B. K. Hinds and J. McCartney (1990), Interactive Garment Design, The Visual Computer, Springer-Verlag, 6, pp 53-61, and H. N. Ng, R. L. Grimsdale and W. G. Allen (1995), A System for Modelling and Visualization of Cloth Materials, Computers and Graphics, Pergamon Press/Elsevier Science, 19(3), pp 423-430.
In this same field, US2001/0026272A1 also describes a system and method for designing a wear article for a virtual three-dimensional model object, wherein a wear article can be displayed on the object by comparing three-dimensional data relating to the article and the object to determine the non-intersection thereof. The shape of the wear article is then conformed to the shape of the object using data relating to a material type of the article, which specifies how the wear article may stretch, flex, sag etc. on the virtual model object to better approximate the real-life look and fit of the article.
Outside of the specific field of virtual clothing models WO 01/08102 discloses a computer aided design system for designing geometric objects, which utilizes computational techniques for blending between geometric objects, wherein weighted sums of points on the geometric objects are used in deriving a new blended geometric objects. In a similar vein, U.S. Pat. No. 6,094,202 describes a method of generating new animated objects from a database of existing objects, by selecting those existing objects with the required features for blending together to produce the new object. The extent to which a selected object is incorporated into the new object may be selected by the animator by assigning each selected object with a weight; the new object is then a sum of each of the differences between each of the selected objects and a base object multiplied by the respective weights.
From a review of the above it should be apparent that whilst the dynamic physical simulation of cloth dynamics can produce very good cloth simulation results, the computational intensity required to perform dynamic cloth-dynamics simulations is exceptionally high, and is unsuitable for many consumer level general purpose computers or other processing devices such as personal digital assistants or mobile phones. Furthermore, the computation required is also too high to achieve good performance from server computers running an on-line shopping application, and which may receive many requests for an avatar clothing model from different users in a relatively short time frame. Therefore, in order to overcome this problem, an alternative cloth modelling method is required which is of reduced computational intensity, but which achieves results of substantially similar quality to the existing cloth-dynamics simulation methods.